The present invention relates to an epoxy resin composition and a method for preparing a silane-modified epoxy resin.
Epoxy resins have been used usually in combination with curing agents in the field of electric and electronic materials. The recent development in the electric and electronic material field has been requiring high-performance cured products of epoxy resin compositions. In particular, improved heat resistance is desired.
In order to improve the heat resistance of the cured products of the epoxy resin compositions, the compositions containing glass fibers, glass particles, mica and like fillers in addition to epoxy resins and curing agents are used. However, these methods using fillers can not impart sufficient heat resistance to the resin compositions. By these methods, the transparency of the resulting cured products is deteriorated and the interfacial adhesion between the fillers and epoxy resins is lowered. Thus, the cured products are given insufficient mechanical properties such as elongation rate.
Japanese Unexamined Patent Publication No. 1996-100107 proposes a method for improving the heat resistance of cured products of epoxy resin compositions by using the complex of an epoxy resin and silica. The complex of an epoxy resin and silica is prepared by adding hydrolyzable alkoxysilane to a solution of a partially cured epoxy resin to further cure the partially cured product; hydrolyzing the alkoxysilane to cause solation; and polycondensing the sol to cause gelation. The heat resistance of the cured product prepared from such complex is improved to some extent compared to the cured product of the epoxy resin by itself. However, water contained in the complex or water and alcohols produced during curing cause voids (air bubbles) inside the cured product. Further, increasing the amount of alkoxysilane to further improve the heat resistance of the cured product results in impaired transparency and whitening of the product due to the aggregation of silica produced by sol-gel curing reaction. In addition, solation of a large amount of the alkoxysilane necessitates a large amount of water, which leads to the bends and cracks in the cured product.
Also proposed are a composition which is produced by combining a silane-modified epoxy resin prepared by reacting the epoxy resin with a silicone compound, and a phenol novolac resin as a curing agent (Japanese Unexamined Patent Publication No. 1991-201466); and a composition prepared by combining a silane-modified epoxy resin produced by reacting bisphenol A epoxy resin, tetrabromobisphenol A and a methoxy-containing silicone intermediate, and a phenol novolac resin as a curing agent (Japanese Unexamined Patent Publications No. 1986-272243, No. 1986-272244). However, the cured products of these epoxy resin compositions do not have sufficient heat resistance since the main structural unit of the silicone compound and methoxy-containing silicone intermediate is a diorganopolysiloxane unit which can not produce silica.
An object of the present invention is to provide a novel epoxy resin composition and a method for preparing a silane-modified epoxy resin which is free from the aforementioned problems of the prior art.
Another object of the present invention is to provide a novel epoxy resin composition which is capable of providing cured products having high heat resistance and no voids or cracks using a specific silane-modified epoxy resin, and a method for preparing said silane-modified epoxy resin.
Other objects and features of the present invention will be apparent from the following description.
The present invention provides an epoxy resin composition comprising an alkoxy-containing silane-modified epoxy resin (A) which is obtainable by dealcoholization condensation reaction between a bisphenol epoxy resin (1) and hydrolyzable alkoxysilane (2); and a curing agent (B) for epoxy resin.
Further, the present invention provides a method for preparing an alkoxy-containing silane-modified epoxy resin, the method comprising dealcoholization condensation reaction between the bisphenol epoxy resin (1) and the hydrolyzable alkoxysilane (2).
The inventors of the present invention conducted extensive research to solve the above-mentioned problems of the prior art. Consequently, the inventors found the following: by using the epoxy resin composition comprising a specific silane-modified epoxy resin (A) obtained by dealcoholization condensation reaction of a bisphenol epoxy resin (1) and hydrolyzable alkoxysilane (2), and a curing agent (B) for epoxy resin, an epoxy resin-silica hybrid having high heat resistance and no voids or cracks can be obtained as a cured product. The present invention was accomplished based on this novel finding.
The raw material of the alkoxy-containing silane-modified epoxy resin (A) of the present invention, namely bisphenol epoxy resin (1), can be obtained by the reaction between bisphenols and epichlorohydrin or xcex2-methylepichlorohydrin and like haloepoxides. Examples of the bisphenols include those obtained by the reaction between phenol or 2,6-dihalophenol and formaldehyde, acetaldehyde, acetone, acetophenone, cyclohexanone, benzophenone and like aldehydes or ketones; those obtained by oxidation of dihydroxyphenylsulfide with a peracid; and those obtained by etherification reaction of one or more hydroquinones.
In addition, the bisphenol epoxy resin (1) has a hydroxyl group which can form silicic acid ester by dealcoholization condensation reaction with the hydrolyzable alkoxysilane (2). Not all the molecules which constitute the bisphenol epoxy resin (1) need to have the hydroxyl group, but the bisphenol epoxy resin (1) itself needs to have the hydroxyl group.
The epoxy equivalent of the bisphenol epoxy resin (1) differs depending on the structure of the bisphenol epoxy resin (1). Therefore, the bisphenol epoxy resin (1) having an epoxy equivalent suitable for its application may be selected. Usually, the epoxy equivalent is preferably about 180 to about 5,000 g/eq. The epoxy equivalent lower than 180 g/eq decreases the amount of alcoholic hydroxyl groups which react with the hydrolyzable alkoxysilane (2) in the epoxy resin molecule. This leads to the reduced formation of the bonds between the epoxy resin (1) and alkoxysilane (2) caused by dealcoholization reaction. As a result, in the epoxy resin-silica hybrids produced when the alkoxy-containing silane-modified epoxy resin (A) is cured with the curing agent (B), insufficient bonding between the silica and epoxy resin occurs. This prevents silica from being uniformly dispersed in the resin. Thus, the cured product is likely to be unfavorably whitened because of the phase separation of the silica and epoxy resin in the product. The epoxy equivalent higher than 5,000 g/eq increases the number of hydroxyl groups in the epoxy resin molecule. Thus, the epoxy resin is likely to disadvantageously undergo gelation during the dealcoholization condensation reaction with multifunctional hydrolyzable alkoxysilane (2). The above-specified epoxy equivalent of 180 to 5,000 g/eq corresponds to a number average molecular weight of 360 to 10,000.
As the bisphenol epoxy resin (1), bisphenol A epoxy resin obtained by using bisphenol A is particularly preferable because of its wide applicability and inexpensiveness.
The above bisphenol A epoxy resin is a compound represented by the formula 
wherein the average of m is 0.07 to 16.4. The epoxy resin of the formula (I) may contain molecules for which m is 0 provided that it also contains molecules for which m is 1 or greater.
An epoxy compound having reactivity with the hydrolyzable alkoxysilane (2) may be used in combination with the bisphenol epoxy resin (1). Examples of the epoxy compound include glycidyl ester epoxy resins obtained by reacting phthalic acid, dimer acid and like polybasic acids with epichlorohydrin, and glycidol and the like. The amount of the epoxy compound to be used in combination is usually about 30 parts by weight or lower, based on 100 parts by weight of the bisphenol epoxy resin (1).
Furthermore, the hydrolyzable alkoxysilane (2) which forms the alkoxy-containing silane-modified epoxy resin (A) of the present invention includes, for example, a compound represented by the formula
R1pSi(OR2)4xe2x88x92pxe2x80x83xe2x80x83(II)
(wherein p is 0 or 1; R1 represents a C1-C8 alkyl group, aryl group or unsaturated aliphatic hydrocarbon group which may have a functional group directly bonded to a carbon atom; R2 represents a hydrogen atom or a lower alkyl group and R2""s may be the same or different from each other) or partial condensates thereof. Examples of the above functional group include vinyl group, mercapto group, epoxy group, glycidoxy group and the like. The lower alkyl group includes a straight-chain or branched-chain alkyl group which has 6 or less carbon atoms.
Examples of such hydrolyzable alkoxysilane (2) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, tetrabuthoxysilane and like tetraalkoxysilanes; methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltributhoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 3,4-epoxycyclohexylethyltrimethoxysilane, 3,4-epoxycyclohexylethyltrimethoxysilane and like trialkoxysilanes; or partial condensates of these compounds.
Among these compounds, preferable are tetramethoxysilane, tetraethoxysilane and like tetraalkoxysilanes or partial condensates thereof. Particularly preferable is poly(tetramethoxysilane) which is a partial condensate of tetramethoxysilane represented by the formula 
wherein the average of n is 1 to 7. The poly(tetramethoxysilane) represented by the formula (III) may contain a molecule in which n is 0 provided that the average of n is 1 or greater. The number average molecular weight of the poly(tetramethoxysilane) is preferably about 260 to about 1,200. In addition, the poly(tetramethoxysilane) is not toxic unlike tetramethoxysilane.
In the formula (III), n represents the average number of repeating units. When the value of n is less than 1, the amount of toxic tetramethoxysilane contained in the poly(tetramethoxysilane) increases. Accordingly, discharge of tetramethoxysilane together with methanol is likely to occur during demethanolization reaction. This is unfavorable in terms of safety and sanitation. When the value of n is greater than 7, the solubility of the poly(tetramethoxysilane) is lowered and the poly(tetramethoxysilane) tends to be insolubilized in the bisphenol epoxy resin (1) and organic solvents. This may unfavorably lower the reactivity between the poly(tetramethoxysilane) and the bisphenol epoxy resin (1).
As the hydrolyzable alkoxysilane (2), those mentioned as examples in the above can be used without any restriction. When using trialkoxysilanes or their condensates, it is preferable that they are usually used in a proportion of 40% by weight or lower of the hydrolyzable alkoxysilane (2) in combination with tetraalkoxysilanes or their partial condensates.
The alkoxy-containing silane-modified epoxy resin (A) of the invention is prepared by dealcoholization condensation reaction between the above bisphenol epoxy resin (1) and the hydrolyzable alkoxysilane (2). This reaction produces said silane-modified epoxy resin in which part or all of the hydroxyl groups of the bisphenol epoxy resin are modified with the hydrolyzable alkoxysilane.
The used ratio of the bisphenol epoxy resin (1) to the hydrolyzable alkoxysilane (2) is not limited insofar as alkoxy groups substantially remains in the resulting alkoxy-containing silane-modified epoxy resin (A). The weight ratio of the hydrolyzable alkoxysilane (2) calculated as silica to the bisphenol epoxy resin (1) is preferably in the range of 0.01 to 3. In this specification, the weight calculated as silica can be calculated by multiplying the mole number of Si atoms of the hydrolyzable alkoxysilane and the molecular weight of silica (R1SiO1.5 or SiO2).
However, when the bisphenol epoxy resin (1) is a macromolecular resin having an epoxy equivalent of 800 or greater and the ratio of an alkoxy equivalent of the hydrolyzable alkoxysilane (2)/a hydroxyl equivalent of the bisphenol epoxy resin (1) is about 1 (approximately equal in stoichiometry), the dealcoholization reaction is accelerated and therefore thickening and gelation of the solution may occur. In this case, the progress of the dealcoholization reaction needs to be controlled. Specifically, the above equivalent ratio is preferably adjusted to be lower than 1 or higher than 1 so that one of the hydroxyl equivalent of the bisphenol epoxy resin (1) and the alkoxy equivalent of the hydrolyzable alkoxysilane (2) is greater than the other. In particular, the above equivalent ratio is preferably adjusted to lower than 0.8 or higher than 1.2.
Further, when a macromolecular resin having an epoxy equivalent of 400 or higher is used as the bisphenol epoxy resin (1); the poly(tetramethoxysilane) of the above formula (a) is used as the hydrolyzable alkoxysilane (2); or the above equivalent ratio is about 1, it is not favorable to conduct the dealcoholization condensation reaction until either of the hydroxyl group of the bisphenol epoxy resin (1) or the alkoxy group of the hydrolyzable alkoxysilane (2) completely disappears. If either of (1) or (2) completely disappears, the molecular weight of the resulting product excessively increases in the reaction system. This may lead to thickening or gelation of the resulting product. In this case, thickening and gelation is prevented by stopping the dealcoholization reaction in the course of reaction or by other manners. For example, the reaction can be stopped in the manners of refluxing effluent alcohol when the thickening starts to adjust the amount of alcohol removed from the reaction system, cooling the reaction system or like manners.
The silane-modified epoxy resin (A) can be prepared, for example, by mixing the above-mentioned components and heating the mixture to remove produced alcohol to cause dealcoholization condensation reaction. The reaction temperature is about 50xc2x0 C. to about 130xc2x0 C., preferably about 70xc2x0 C. to about 110xc2x0 C., and the reaction time is about 1 to about 15 hours. This reaction is preferably conducted under a substantial anhydrous condition to prevent polycondensation reaction of the hydrolyzable alkoxysilane (2) itself.
In the dealcoholization condensation reaction, conventionally known catalysts which do not cause ring opening of an epoxy ring may be used to accelerate the reaction. Examples of such catalysts include lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, barium, strontium, zinc, aluminum, titanium, cobalt, germanium, tin, lead, antimony, arsenic, cerium, boron, cadmium, manganese and like metals; and oxides, organic acid salts, halides, alkoxides of these metals. Among them, organotin and tin organoate are particularly preferable. More specifically, dibutyltin dilaurate, tin octoate and the like are effective.
The above reaction can be performed in a solvent or without a solvent. The solvent is not particularly limited insofar as it is an organic solvent which can dissolve the bisphenol epoxy resin (1) and hydrolyzable alkoxysilane (2) and is inactive to these compounds. Examples of such organic solvent include dimethylformamide, dimethylacetamide, tetrahydrofuran, methyl ethyl ketone and like aprotic polar solvents.
The thus-obtained alkoxy-containing silane-modified epoxy resin (A) of the present invention contains, as a main component, the bisphenol epoxy resin (1) having the hydroxyl group modified with silane. The alkoxy-containing silane-modified epoxy resin (A) of the invention may contain unreacted bisphenol epoxy resin (1) and hydrolyzable alkoxysilane (2). The unreacted hydrolyzable alkoxysilane (2) can be converted to silica by hydrolysis and condensation. To promote the hydrolysis and condensation, a small amount of water may be added to the alkoxy-containing silane-modified epoxy resin (A) when used. The alkoxy-containing silane-modified epoxy resin (A) of the present invention contains alkoxy groups derived from the hydrolyzable alkoxysilane (2) in its molecule. The amount of the alkoxy groups is not critical. The alkoxy groups are necessary for forming a network-like siloxane bond therebetween by evaporation of solvents, heat treatment, or reaction with water (moisture) and for providing a mutually bonded cured product. Therefore, 50 to 95 mol %, preferably 60 to 95 mol % of the alkoxy groups of the hydrolyzable alkoxysilane (2), which is a reaction material, is left unreacted in the alkoxy-containing silane-modified epoxy resin (A). Such cured product has gelated fine silica portions (higher network structure of the siloxane bond).
The alkoxy-containing silane-modified epoxy resin (A) of the invention can be used for various applications without any restriction. In particular, the alkoxy-containing silane-modified epoxy resin (A) is preferably used as an epoxy resin composition of the present invention by combining with the curing agent (B) for epoxy resin.
When using the epoxy resin composition of the invention for various applications, various epoxy resins may be used in combination depending on the application. Examples of such epoxy resin include the above bisphenol epoxy resin (1) mentioned as the constituent of the present invention, orthocresol novolac epoxy resin, phenol novolac epoxy resin and like novolac epoxy resins; glycidyl ester epoxy resins obtainable by reacting phthalic acid, dimer acid and like polybasic acids with epichlorohydrin; glycidyl amine epoxy resin obtainable by reacting diaminodiphenylmethane, isocyanuric acid or like polyamines with epichlorohydrin; and linear aliphatic epoxy resin and alicyclic epoxy resin obtainable by oxidizing olefin bond with peracetic acid and like peracids. Low molecular weight epoxy compounds such as glycidol and the like may also be used in combination.
As the curing agent (B) for epoxy resin may be unrestrictedly used those commonly used as curing agents for epoxy resin such as phenol resin curing agents, polyamine curing agents, polycarxylic acid curing agents and the like. Specifically, phenol resin curing agents include phenol novolac resin, bisphenol novolac resin, poly p-vinylphenol and the like. The polyamine curing agents include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dicyandiamide, polyamideamine, polyamide resin, ketimine compound, isophorone diamine, m-xylenediamine, m-phenylenediamine, 1,3-bis(aminomethyl)cyclohexane, N-aminoethylpiperazine, 4,4xe2x80x2-diaminodiphenylmethane, 4,4xe2x80x2-diamino-3,3xe2x80x2-diethyldiphenylmethane, diaminodiphenylsulfone and the like. The polycarboxylic acid curing agents include phthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, 3,6-endomethylenetetrahydrophthalic anhydride, hexachloroendomethylenetetrahydrophthalic anhydride, methyl-3,6-endomethylenetetrahydrophthalic anhydride and the like. The above epoxy resin curing agent (B) not only reacts with the epoxy ring to cause ring opening and curing, but also works as a catalyst for the siloxane condensation reaction of the alkoxysilyl sites in the alkoxy-containing silane-modified epoxy resin (A) and the alkoxy groups in the unreacted hydrolyzable alkoxysilane. Among the above curing agent (B) for epoxy resin, the polyamine curing agents are the most suitable as a curing catalyst for alkoxysilyl sites and alkoxy groups. Thus, the polyamine curing agents are the most suitable as a curing agent (B) for the alkoxy-containing silane-modified epoxy resin (A).
The used ratio of the curing agent (B) for epoxy resin to the alkoxy-containing silane-modified epoxy resin (A) is usually such that the equivalent ratio of the functional groups having active hydrogen in the curing agent to the epoxy groups of the alkoxy-containing silane-modified epoxy resin (A) is about 0.2 to 1.5. Examples of the above functional groups include amino group, acid anhydride group, phenolic hydroxyl group, carboxylic group, sulfonic group and the like.
In addition, the above epoxy resin composition may contain an accelerator for curing reaction between the epoxy resin and the curing agent. Examples of the accelerator include 1,8-diaza-bicyclo[5.4.0]undecene-7,triethylenediamine, benzyldimethylamine, triethanolamine, dimethylaminoethanol, tris(dimethylaminomethyl)phenol and like tertiary amines; 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-heptadecylimidazole and like imidazoles; tributylphosphine, methyl diphenylphosphine, triphenyl phosphine, diphenyl phosphine, phenyl phosphine and like organic phosphines; tetraphenylphosphonium* tetraphenyl borate, 2-ethyl-4-methylimidazole*tetraphenyl borate, N-methylmorpholine*tetraphenyl borate and like tetraphenyl borates. The accelerator is preferably used in an amount of 0.1 to 5 parts by weight relative to 100 parts by weight of the epoxy resin.
The concentration of the epoxy resin composition can be suitably controlled using a solvent. The solvent may be the same as that used for preparing the alkoxy-containing silane-modified epoxy resin (A). The epoxy resin composition may also contain fillers, mold releasing agents, surface modifiers, fire retardants, viscosity modifiers, plasticizers, antibacterial agents, antimolds, leveling agents, antifoaming agents, coloring agents, stabilizers, coupling agents, etc., if necessary. These additives may be used insofar as it does not lower the effects of the present invention.
The present invention can provide a cured product of an epoxy resin composition with high heat resistance and without voids (air bubbles) or the like.
The epoxy resin composition of the present invention is useful as an IC sealing material, an epoxy resin laminate plate, a coating composition, an adhesive, a coating for electric and electronic materials and for various other applications.